1. Field of the Invention
The present invention relates to a video transmission apparatus that transmits video data for each video frame group including one or more encoded video frames.
2. Description of the Related Art
For example, Japanese Patent Laid-Open No. 2005-086362 discloses a technique in which in a case where video transmission is delayed or interrupted due to network trouble or the like, a past video frame group that was not able to be transmitted is eliminated and the latest video frame group is transmitted so that delay can be reduced.
In a technique disclosed in Japanese Patent Laid-Open No. 2004-056819, in addition to a first encoding unit configured to generate inter-frame predictive coded first video data, a second encoding unit configured to generate intra-frame predictive coded second video data is provided. At the resumption of transmission, the second video data is transmitted as a complement to the first video data, and the second video data is decoded in advance. Consequently, even if transmission is resumed from a middle portion of a group of pictures (GOP), video data can be correctly decoded and played back.
However, in a system disclosed in Japanese Patent Laid-Open No. 2004-056819, a special function of receiving two types of video data and switching between them needs to be incorporated into a reception apparatus. Thus, it is difficult for the reception apparatus to play back video data by using a general playback process. In general, video data is played back using a media player such as QuickTime Player or Windows Media Player. Furthermore, it is necessary for a transmission apparatus to include a plurality of encoding units supporting different encoding methods. Thus, problems relating to complication of the hardware configuration and an increase in the load of software processing occur.
In the case of an MP4 file format, a movie fragment (hereinafter, referred to as a “fragment”), which is the unit of transmission, may be defined as in one of the following options:
(1) A group of video object planes (GOV) including video frames from a reference video frame that is encoded without inter-frame prediction to the video frame that is immediately before the next reference video frame, is defined as a fragment.
(2) Each of a plurality of sections obtained by dividing a GOV is defined as a fragment.
In the case of option (1), a fragment always starts from an I-frame (intra-coded frame: a video frame that has been encoded using only data within the frame). However, in the case of option (2), some fragments start from a video frame other than an I-frame, such as a P-frame (predicted frame: a video frame holding differential information on the immediately preceding video frame).
Thus, in a method for simply skipping to the latest fragment to resume transmission as in Japanese Patent Laid-Open No. 2005-086362, in a case where a fragment is defined as in option (2), decoding cannot be performed and an error occurs in a general playback method.
Even in such a case, when a reception apparatus includes a decoding unit having a special function of ignoring video frames in a fragment not including an I-frame up to the frame immediately before the next I-frame, video playback can be continued. However, general network media players do not include a decoding unit having such a special function. In addition, even if a reception apparatus independently includes a decoding unit having such a function, complicated processing is required, resulting in an increase in the processing load.
In addition, in a case where the length of a GOV is long (the number of frames is large), when transmission is resumed from the fragment starting from a P-frame that is immediately after a fragment starting from an I-frame, video is stopped for a long period of time until the next I-frame appears.